A fuel cell is an energy conversion device that generates electricity and heat by electrochemically combining a gaseous fuel, for example, hydrogen, carbon monoxide, or a hydrocarbon, with an oxidant such as air or oxygen, across an ion-conducting electrolyte. The fuel cell converts chemical energy into electrical energy, which may then be used by a high-efficiency electric motor, or stored. A solid oxide fuel cell (SOFC) is frequently constructed of solid-state materials, typically utilizing an ion conductive oxide ceramic as the electrolyte. A conventional electrochemical cell in a SOFC is comprised of an anode and a cathode with an electrolyte disposed therebetween. The oxidant passes over the oxygen electrode or cathode while the fuel passes over the fuel electrode or anode, generating electricity, water, and heat.
In a typical SOFC, a fuel flows to the anode where it is oxidized by oxygen ions from the electrolyte, producing electrons that are released to the external circuit, and mostly water and carbon dioxide are removed in the fuel flow stream. At the cathode, the oxidant accepts electrons from the external circuit to form oxygen ions. The oxygen ions migrate across the electrolyte to the anode. The flow of electrons through the external circuit provides for consumable or storable electricity. However, each individual electrochemical cell generates a relatively small voltage. Higher voltages may be attained by electrically connecting a plurality of electrochemical cells in series to form a stack.
U.S. Pat. No. 6,737,182, the disclosure of which is incorporated herein by reference, discloses a solid oxide fuel cell stack comprising an electrochemical cell that has an electrolyte disposed between and in ionic communication with a first and second electrode, and an interconnect that is in fluid and thermal communication with at least a portion of the electrochemical cell, the interconnect being configured to receive electrical energy and thereby act as a heating element.
U.S. Patent Application Publication No. 2005/0153190, the disclosure of which is incorporated herein by reference, discloses a solid oxide fuel cell stack that comprises flexible thin foil interconnect elements and thin spacer elements that can conform to nonplanarities in the stack's electrolyte elements, thereby avoiding the inducing of torsional stresses in the electrolyte elements.